1. Field of the Invention
The present invention relates to a method for recycling of old corrugated container (OCC) using flotation and enzymatic hydrolysis and more particularly, to a method for recycling of old corrugated containers enhancing strength without deteriorating drainage, wherein old corrugated containers are treated with floatation and enzymatic hydrolysis.
2. Description of the Prior Art
The total paper production of Republic of Korea amounted to 8 million tons in 1997, and hence Korea became one of the top 10 largest production countries in the world. The production of the base paper for corrugated board essential for packaging goods accounts for more than 30% of the total paper production. Corrugated board as packaging material has the advantage in that printing and processing are easy, the strength to weight ratio is excellent, and recycling is possible. At present, the recycling rate of used paper in Korea is the highest over the world, and in 1995, it was the highest among the top 10 largest paper production countries as 72% [Vital Signs, 1998]. Especially, the base paper of corrugated board is mainly produced from Korean old corrugated container (KOCC), and thus the recycling rate of KOCC is very high. However, there is a problem that the pulp quality is very low while the recycling rate of OCC is high.
The fines content in KOCC, the main source of the corrugated board, amounts to nearly the half of the total stock, and fines content increases as recycling process repeats due to the hornification of fiber. Generally, fines refer to inorganic materials and single fibers smaller than 72%, and they have been the main cause of the declination of productivity because they interfere dewatering of wet web in papermaking process of the base paper.
Meanwhile, there have been attempts to improve the drainage properties of OCC by increasing the headbox concentration of the paper machine or by applying drainage-promoting polymer additives. However, these conventional methods have problems of weakened paper strength and lowered surface properties caused by bad formation. Also, when considering the recent trend that the recycling rate of white water in papermaking process is blocked for water saving and environmental protection, the chemical and biological oxygen demand is likely to increase due to the accumulation of the additives in process water. Therefore, the decreased drainage properties caused by the fines in papermaking process for the base paper of corrugated board are inevitable in the conventional manufacturing technology, as far as KOCC is used for the source material. Thus the development of new environment-friendly paper recycling technology different from conventional one is keenly demanded.
In addition, the strength of base paper of corrugated board could not be increased in case KOCC is used for raw material, because the pump from KOCC has too much fines and contaminants. Although the separation technology of OCC with screen or cleaner to long and short fiber portions has been applied in developed countries [Bliss T., Pump and Paper, 88, 104 (1987); Clark L. E. and Iannazzi F. D., Tappi, 57, 59 (1974)], the said technology is only suitable for high quality OCC comprising good quality of unbleached kraft pulp and semi-chemical pulp. The strength of the base paper of the corrugated board can not be improved, in case low-quality OCC, having more fines content that long fiber portions, is used for main material of the corrugated board, as in Korea.
For this reason, high-quality base paper for corrugated board with excellent strength has been imported until now, and recently the imported amount of high quality base paper of corrugated board has increased rapidly from 166,000 tons in 1995 to 193,000 tons in 1996 [Pulp & Paper International, 39, 65 (1997)]. As mentioned above, there was no alternative other than using 100%-imported unbleached kraft pulp as raw material, and KOCC could not be used with the conventional technology. Actually, in 1996, the total quantity of unbleached kraft pulp imported for the manufacture of kraft paper and various corrugated board amounted to 270,000 tons [Pulp & Paper International, 39, 65 (1997)]. Accordingly, there is a serious demand for the development of new recycling technology which improves the productivity, enhances the strength, and reproduces to high-quality corrugated board by improving the drainage property of KOCC with high fines content.